The present invention relates to PLL (Phase Locked Loop) circuit for use in a radio pager and, more particularly, to a power supply for a PLL circuitry.
A PLL circuit for the above application has customarily been made up of a PLL section including a charge pump circuit, and a power supply section. For miniaturization, the PLL circuit is as constructed as to operate at low voltage and consume great current. However, a higher voltage, e.g., 3 volts has to be applied to the charge pump circuit than to the other circuits in order to enhance the carrier-to-noise (C/N) ratio of oscillation frequency signal. For this purpose, the power supply section is provided with a DC/DC converter. The DC/DC converter, however, undesirably scales up the overall PLL circuit and, therefore, obstructs the miniaturization of a radio pager.